Major current problems in aircraft instrument cooling addressed by this invention include: (1) keeping panel mounted, closely spaced instruments adequately cool so that their function and reliability are not adversely affected by heat; and (2) keeping the temperature of the instrument panel surface within specified limits so that it is tolerable to touch and to prevent excessive amounts of heat from being radiated into the aircraft cabin and placing a burden on the cabin cooling system. These problems have now become acute for aircraft instrument panels. With the increased use of instrumentation for aircraft, there is a requirement to install more and more electronic instruments in a given panel area. Furthermore, the amount of heat generated by each instrument has generally increased as new and improved functions are added. This invention was motivated by these problems and the fact that new standards relating to permissible temperature levels have been imposed, as discussed below.
The most common current cooling technique for aircraft instrument panels is to induce airflow from the space in front of the panel, down and under the panel, and thence up and among the instrument cases projecting behind the panel. The resulting haphazard flow patterns produce non-uniform cooling. In particular, the instruments nearer the top of the panel are reached only by air already heated by the lower instruments, so that the higher instruments are often inadequately cooled. This condition persists in spite of any reasonable increases in airflow.
Special purpose cooling problems are prevalent in non-aircraft environments wherever electrical/electronic equipment is used. For example, U.S. Pat. No. 2,394,060 shows an equipment cabinet for housing electrical discharge devices of the type using enclosed, generally cylindrical envelopes of ionizable medium, such as mercury vapor. In order to promote condensation of the ionizable medium, a single stream of air is made to impinge radially onto the cylindrical surface of the enclosing envelope at the point at which it is desired to effect condensation. The discharge devices are mounted on the exterior side of a wall of a plenum chamber. The higher pressures of the plenum chamber cause a jet of air to pass through an opening in the wall to strike each device. Such localized cooling techniques are relatively ineffective with instruments which tend to generate heat over the entire length and periphery of the instrument case, as do most aircraft instruments. See also U.S. Pat. No. 3,192,306 which shows an electronic equipment rack using plenum chambers with outlet holes for selective delivery of single, relatively large streams of cooling air to specific regions in the rack.